Optical arrangement for producing stereoscopic images

ABSTRACT

The invention is directed to an optical arrangement for stereoscopic viewing of objects ( 8 ) which is outfitted with an imaging system and with at least one lens group ( 1 ) with a fixed focal length which is arranged between the imaging system and a viewed object ( 8 ) for changing the imaging scale.  
     According to the invention, this is achieved in that an adjusting device is provided for changing the position of the lens group ( 1 ) in the direction of the optical axis and, accordingly, for changing the distance c between the lens group ( 1 ) and a reference edge ( 4 ) of the imaging system.  
     This makes it possible to adjust different magnifications β′ by actuating the adjusting device or changing the distance c and, therefore, to generate virtual intermediate images of objects ( 8 ) located at various distances within a working range in the imaging plane of the stationary system. Accordingly, very advantageous applications are possible in restoration work, in dental engineering, and so on, in which the enhanced use value achieved by the invention is desired.

[0001] The invention is directed to an optical arrangement forstereoscopic viewing of objects which is outfitted with an imagingsystem and with at least one lens group with a fixed focal length whichis arranged between the imaging system and a viewed object for changingthe imaging scale.

[0002] Optical arrangements used for imaging objects have thepossibility of focusing on these objects and adjusting the imagingfocus. The apparatus provided for this purpose can be categorizedaccording to three basic principles:

[0003] According to a first principle, the object and the imaging systemare moved relative to one another for focusing; that is, either theimaging system is displaced in the direction of the object or,conversely, the object is displaced in the direction of the imagingsystem as, for example, in microscopes in which the objective isdisplaced based on the principle of objective focusing or the objectsupport, or slide, with the object is moved based on the principle oftable focusing.

[0004] In contrast, in a second principle, the focus adjustment iscarried out with a constant distance between the object and imagingsystem in that an optical component of the imaging system is displacedaxially relative to other components of the imaging system and theimaging system is accordingly focused on the object. Binoculars,photographic objectives and video cameras operate on this principle.

[0005] In optical arrangements based on a third principle, thetransmission length is changed by an optical auxiliary system which isarranged between the object to be imaged and the imaging plane of theimaging system. In this way, the object position can be adapted towithout intervention in the internal construction of the imaging systemand without changing the position of the imaging system relative to theobject. The invention described in the following must also be classed inthis category.

[0006] Optical arrangements for stereoscopic imaging of objects inwhich, based on the third principle mentioned above, a supplementaryoptical system in the form of a lens group serving to change the imagingscale is positioned between a fixed imaging system and the object areknown in the art.

[0007] Depending upon the particular application, such supplementarysystems have a positive or a negative focal length. Greenough typemicroscopes in particular are outfitted with supplementary systems suchas these. For example, the “DV 4” and “Stemi 2000” stereomicroscopes byCarl Zeiss Jena GmbH are known in which a fixed magnification factor isachieved with the supplementary system.

[0008] The use of supplementary systems is also known for telescope typestereomicroscopes, for example, the “TECHNIVAL” and “CITOVAL”stereomicroscopes described in Beyer/Riesenberg, “Handbook ofMicroscopy”, Verlag Technik Berlin, third edition, 1998, 348ff. In thiscase, also, the transmission length is defined by the choice ofmagnification range and a change is possible only by changing thesupplementary system or exchanging the base objective.

[0009] This is disadvantageous for applications in which a variabledistance to the object to be viewed must be spanned by a stationaryoptical arrangement, which is required, for example, in restorationwork. In this case, an upright, non-reversed image is needed, which canonly be achieved with an imaging scale greater than “zero”.

[0010] As is well known, either a real intermediate image or a virtualintermediate image is generated in the object plane of thestereomicroscope for this purpose. The invention described in thefollowing is directed to the generation of virtual intermediate images.

[0011] Based on the prior art described above, it is the object of theinvention to further develop arrangements for stereoscopic imaging ofobjects of the type described above in such a way that the workingdistance from the object to be viewed can be varied in a simple mannerand which accordingly makes it possible to observe objects at variousdistances without fatigue.

[0012] According to the invention, this object is met in that anadjusting device is provided for changing the position of the lens groupin the direction of the optical axis and, accordingly, for changing thedistance c between the lens group and a reference edge of the imagingsystem.

[0013] This makes it possible to adjust different magnifications β′ byactuating the adjusting device or changing the distance c and,therefore, to generate virtual intermediate images of objects located atvarious distances within a working range in the imaging plane of thestationary system. Accordingly, very advantageous applications arepossible in restoration work, in dental engineering, and so on, in whichthe enhanced use value achieved by the invention is desired.

[0014] The change in the transmission length caused by changing thedistance c by an amount Δc depends upon the focal length of the lenssystem and, therefore, upon the initial magnification β′ and causes achange in magnification toward β′=1. An especially advantageous actionresults with a relatively small initial magnification β′.

[0015] A change in magnification β′ or focus displacement takes placefor all focal lengths f′_(group) when the lens group is positionedbetween the imaging system and the focal plane of the imaging system.The greatest dynamics result from changing the back focal distance a ata maximum distance c.

[0016] In a particularly advantageous construction of the invention, thelens group comprises two lenses with the following characteristics:

[0017] radii of the optically active interfaces or boundaries:R₁=−67.722 mm; R₂=56.249 mm; R₃=−3867 mm;

[0018] vertex distances of the optically active boundaries on theoptical axis: D₁=2.8 mm; D₂=5.75 mm;

[0019] principal wavelength λ=546 nm;

[0020] refractive indices for the principal wavelength: Ne₁=1.60629;Ne₂=1.65285

[0021] dispersion (Abbe number): νe₁=53.35; νe₂=33.59.

[0022] When a lens group of this kind is placed in front of the imagingsystem, changes in magnification β′ or in focal distances a and b can beachieved in the following way by varying the distance c: MagnificationBack focal Object focal Distance c β′ distance a distance b Distance Ac₁ 0.3 a₁ = 93.74 b₁ = 294.5 — c₂ 0.4 a₂ = 81.04 b₂ = 189.1 A₂ = 92.7 c₃0.5 a₃ = 69.27 b₃ = 125.9 A₃ = 144.13

[0023] In a particularly preferable manner, the optical arrangementaccording to the invention is constructed as a Greenough typestereomicroscope and the lens group, including the adjusting device, isadapted to the base body of the stereomicroscope.

[0024] The invention will be described more fully in the following withreference to an embodiment example. In the accompanying drawings:

[0025]FIG. 1 shows the example of a lens group comprising two lenses,designed for a Greenough stereomicroscope;

[0026]FIG. 2 is a schematic view showing the positioning of the lensgroup between the imaging system and object of a Greenoughstereomicroscope.

[0027]FIG. 1 shows the lens group 1 comprising two lenses 2 and 3. Thelens group 1 has a negative focal length and is designed andachromatized for the principal wavelength λ=546 nm. The optically activeboundaries of the lens 2 have radii R₁=−67.722 mm and R₂=56.249 mm. Lens3 is constructed with radii R₂=56.249 mm and R₃=−3867 mm. The vertexdistances of the optically active boundaries on the optical axis areD₁=2.8 mm for lens 2 and D₂=5.75 mm for lens 3.

[0028] Further, the material of lens 2 has an index of refraction ofNe₁=1.60629 and a dispersion of νe₁=53.35. These characteristic valuesare Ne₂=1.65285 and νe₂=33.59 for lens 3.

[0029]FIG. 2 shows how the lens group 1 is positioned relative to object8 and microscope beam paths 5 and 6. The position of a reference edge 4at the imaging system is indicated in the form of a working line.

[0030] The sum c+a is constant and is determined by the free workingdistance of the imaging system. The distance c between reference edge 4and lens group 1 is variable, wherein an adjusting device, not shown inthe drawing, is used for changing the position of the lens group 1.Adjusting devices of this kind and their coupling to opticalsubassemblies which are variable in position are adequately known sothat a more detailed description can be dispensed with.

[0031] For purposes of explaining operation, the drawing also shows theaxial distance a between the vertex plane of the lens group 1 and theimage plane 7 in which the optical system generates the image of anobject 8 to be observed. The distance between the lens group 1 and theobject 8 is designated as distance b. In this case, distance acorresponds to the back focal distance and distance b corresponds to theobject focal distance.

[0032] The quantities for distances a and b are associated by thefollowing equations:

|1/(−a ₁ −k ₁)−1/(b ₁ −k ₂)−1/f′ _(group)|<0.02   (I)

|−(−a−k ₁)/(b−k ₂)−β|<0.02   (II)

[0033] with constants k₁ and k₂ and focal length f′_(group) similar tothe paraxial equations. Equation (I) defines the capture area, equation(II) formulates the dynamics of the magnification when the transmissionlength is changed. For the present example: k₁=−2.52, k₂=−3.29 andf′_(group)=−126.01.

[0034] The distance A between the reference edge 4 and the object 8 isdefined by A=c+b+D₁+D₂ (see FIG. 2). When objects located at differentdistances A₂ or A₃ are to be observed, for example, the optical imagingcan be adapted, according to the invention, to the different distances Aby actuating the adjusting device, i.e., by varying the distance c.

[0035] For example, when adjusting to distance c₁, an object is focusedwith magnification β′=0.3. In order to view an object which is located,for instance, at a distance from the reference edge 4 that is smaller bythe amount A₂=92.7, this object is focused with a magnification β′=0.4as can be seen from the following table which is also contained in claim3: Magnification Back focal Object focal Distance c β′ distance adistance b Distance A c₁ 0.3 a₁ = 93.74 b₁ = 294.5 — c₂ 0.4 a₂ = 81.04b₂ = 189.1 A₂ = 92.7 c₃ 0.5 a₃ = 69.27 b₃ = 125.9 A₃ = 144.13

[0036] Accordingly, depending on the given working distance between theobserver and the object or depending on the object focal distance b, thedistance c can be changed within an area which causes a change in theimaging scale by a factor of 0.3 in b₁, by a factor of 0.4 in b₂ and bya factor of 0.5 in b₃.

[0037] The term “imaging scale” is used in the preceding description ofthe invention in the sense of the size ratios of the intermediate imageand object.

[0038] The arrangement according to the invention also enablesobservation when the focusing principles (change in the distance betweenthe imaging system and object) which are conventional per se instereomicroscopes are not applicable, as is frequently the case inrestoration work, for example.

[0039] Therefore, as was described above with reference to an embodimentexample of the invention, application of a variable supplementary systemfor bridging variable transmission lengths is preferred for restorationwork and also in process monitoring with fixed instrument assemblies.Further, it is advantageously used when objects of various sizes areobserved and documented successively in time in the fields of qualitycontrol, botany, criminalistics, and the like. The lens group (1) ispreferably designed for a focal length range f′_(group) of${- 0.75} \leq \frac{a_{1}}{f_{group}^{\prime}} \leq 1.4$

[0040] with the greatest possible back focal distance a₁.

REFERENCE NUMBERS

[0041]1 lens group

[0042]2,3 lens

[0043]4 reference edge

[0044]5,6 microscope beam path

[0045]7 image plane

[0046]8 object

[0047] a, b, c distance

[0048] R₁, R₂, R₃ radius

[0049] D₁, D₂ vertex distance

[0050] N₁, N₂ index of refraction

[0051] ν₁, ν₂ dispersion

1. Optical arrangement for stereoscopic viewing of objects which isoutfitted with an imaging system and with at least one lens group (1)with a fixed focal length which is arranged between the imaging systemand a viewed object for changing the imaging scale, wherein the lensgroup (1) and its position relative to the imaging system are designedfor generating an intermediate image, and an adjusting device isprovided for changing the position of the lens group (1) in thedirection of the optical axis and, accordingly, for changing thedistance c between the imaging system and the lens group (1), so thatthe imaging scale is variable in ranges greater than “zero”.
 2. Opticalarrangement according to claim 1, characterized in that the followingchanges in magnification and in focal distances occur by changing thedistance c: Magnification Back focal Object focal Distance c β′ distancea distance b Distance A c₁ 0.3 a₁ = 93.74 b₁ = 294.5 — c₂ 0.4 a₂ = 81.04b₂ = 189.1 A₂ = 92.7 c₃ 0.5 a₃ = 69.27 b₃ = 125.9 A₃ = 144.13


3. Optical arrangement according to claim 1, characterized in that thelens group (1) comprises two lenses (2, 3) with the followingcharacteristics: radii of the optically active boundaries: R₁=−67.722mm; R₂=56.249 mm; R₃=−3867 mm; vertex distances of the optically activeboundaries on the optical axis: D₁=2.8 mm; D₂=5.75 mm; principalwavelength λ=546 nm; refractive indices for the principal wavelength:Ne₁=1.60629; Ne₂=1.65285 dispersion (Abbe number): νe₁=53.35; νe₂=33.59.4. Optical arrangement according to one of the preceding claims,constructed as a stereomicroscope, wherein the lens group (1), includingthe adjusting device for changing distance c, is adapted to the basebody of the stereomicroscope.